Ni Hao, Kai-lan is based on the childhood memories of the show's creator Karen Chau growing up in a bicultural (Chinese-American) household. “Ni hao” means “Hello” in Mandarin, and Kai-Lan is the Chinese name Chau was given at birth, which was later anglicized to Karen. It was also based on the classic short series Downward Doghouse.

The setting of the show appears to be China or Ancient China throughout most episodes. However, it's revealed in the Season 1 finale that they all live in California, possibly in Chinatown. It appears most of the characters aren't Chinese. This is not explained. Ni Hao, Kai-lan introduces its viewers to the Mandarin Chinese language, along with elements of Chinese culture and values, multiculturalism (through the diverse backgrounds of Kai-lan's friends), and intergenerational families (e.g., Kai-lan and her relationship with Ye Ye).

Episodes generally feature breaking the fourth wall, 11 minutes of interactivity,[1] a target word that is repeated multiple times,[2] a few words of Mandarin Chinese vocabulary, one or more of Kai-lan's friends having a negative emotional response to some action or activity (problem), Kai-lan thinking out loud (observation), cause-and-effect problem solving, and before saying goodbye (at the end of each episode), Kai-lan says, "You make my heart feel super happy!" Later installments added Kai-lan saying this phrase in Mandarin after she said it in English: "Ni rang wo hao kai xin!"

Kai-Lan is the host and main character, a playful, adventurous young girl with a big heart. She speaks both English and Mandarin Chinese, and she is eager to share her language, her culture, and her playtime with her animal friends and the viewers at home. Kai-Lan is a natural leader but she is also thoughtful and caring with a gift for helping her friends when they really need her. Her favorite animal is a dinosaur and in her music group, she plays her tambourine.

Ye-Ye (simplified Chinese: 爷爷; traditional Chinese: 爺爺; pinyin: yéye, "paternal grandfather") is Kai-lan's grandfather and legal guardian. He was born in Hong Kong and lovingly passes on his exciting traditions to his granddaughter. He provides Kai-lan with gentle guidance, leading her to find her own answers, at her own pace. (Kai-lan's parents and other grandparents are not known.) He can play the tuba. He also enjoys picking apples and making dumplings for Kai-lan and all her animal friends. He's known to pop out of places unexpectedly, but the gang just gets used to it after a while.

Rintoo is a rambunctious yellow-and-black tiger with a lisp who often acts before he thinks. He likes to play rough but when it comes to his friends, he's willing to compromise. He loves dragons and racing racecars. Even though he is with Hoho most of the time, his actual best friend is Tolee. He plays the xylophone in Kai-Lan's music group. He got hurt twice in the series, one was spraining his ankle on a rock on Halloween, and another was being punched in the leg by Hoho. (He shook that other hit off, however.) He might be a tiger, but he is sweet on the inside.

Tolee is a gray koala who loves pandas and fruit (especially apples, bananas, and pineapples). He is intelligent and always thinks before he acts and sometimes worries too much, but he never lets that stop him from having a great time with his friends. Kai-Lan and her friends can always rely on him for good ideas. Tolee also has a stuffed panda he affectionately named Pandy, and Tolee loves Pandy so much he can't imagine being without him. The unimaginable, however, happens in Pandy's Puddle when he accidentally drops Pandy into a mud-filled puddle, the reason being he was trying to pull up a very large Chinese turnip. Resulting in Pandy having to be put into a washing machine to get clean. Tolee did not like the idea of being without Pandy and cried. But then felt better by having a picture of him and Pandy, and he also made him a card, later, he got him back. He is the vocalist in Kai-Lan's music group. His love for pandas culminated in the two part episode "Kai-Lan's Great Trip to China" when the group traveled to China to meet a whole family of pandas including baby Xiao Xi Gua (Little Watermelon).

Hoho the white monkey is the youngest of Kai-lan's friends, so when he participates in activities, he often goes first. He's full of boundless energy and nothing makes him happier than being the center of attention. Whenever he jumps a spring sound can be heard. He can often be found jumping on his friends' heads or playing his turntables as the resident DJ in Kai-Lan's music group. The turntables are normally stored in a tree when not in use. Aside from his turntables and his friends, Hoho's favorite thing happens to be bananas. Hoho can sometime have a fiery temper when he doesn't get his way.

Lulu is a pink rhino. She has a red balloon tied around her horn that helps her fly in the sky. Lulu is very energetic and sweet. She loves her friends. When her friends are in trouble, Lulu is the one in the group who stays calms, remains positive, and thinks of a solution to the problem. Lulu is always seen as being there to help her friends. Lulu's home is castle in the sky. She is best friends with Kai-Lan. Lulu plays the piano in Kai-Lan's music group. Her favorite fruit is the lychee. Some of Lulu's favorite games include: dancing, playing house, having tea parties, and dressing up like a fairy.

At the start of almost every episode, Kai-Lan wakes up Mr. Sun so she can start her day. With the help of the viewer, Mr. Sun rises and showers down smiling sun fuzzies to Kai-Lan and she gets tickled by them. He also knows how to play the French horn, so Kai-Lan and the lady bugs (playing the pi-pa) join him as a little music group at the beginning of Tolee's Rhyme Time and later joins Kai-Lan and her friends in the music show.

In one corner of Kai-Lan's backyard is a teeming mini-metropolis of ants called Ant City. The ants serve very important roles in the community: they deliver mail, they build things, and they love to play with Kai-Lan and her friends. San San is their leader along with his two right-hand ants, Bubu and Fufu.

San San is voiced by Zachary Gordon, Bubu is voiced by Luke Manriquez, and Fufu is voiced by Kyla Rae Kowalewski.

Stompy the Elephant is a big, playful blue elephant who first appears in "Safari Pals." Nothing makes Stompy happier than being able to play with his friends. He is also known by some as Spouty or Trunky because of his long trunk.
Stompy is voiced by Hsiang Lo.

Hula ducks who don't speak but dance and quack are in episodes sometimes. They're very conservative as shown when they made pumpkin pie out of a broken pumpkin.

An unnamed bat makes a few appearances as an audience member or a background character. He is believed to live in a bathroom.

GuNaiNai is Kai-Lan's Great Aunt and YeYe's sister. She appears in "Kai-Lan's Trip to China."
GuNaiNai is voiced by Ming-Na Wen.

Xiao Xi Gua ("little watermelon") is a baby panda. He appears in "Kai-Lan's Trip to China."

The Peeking Mice are little, black mice who are often seen playing music.
They are voiced by assorted members of the cast.

The Scotland Rabbits playing tunes on his bagpipes.

Mr. Hoppy is a green frog who speaks in ribits. In Kai-Lan's carnival, he has darker eyes, shown without a bowtie, talks completely and owns a game booth called "Mister Hoppy's Hop-and-Splash" where the player has to throw a ball to sink a lilypad.

The Monkey King is an incredible superhero who asked Kai-Lan and her friends for help in a magical kingdom where the foxes and the bears never talk to each other. He appears in "Princess Kai-Lan." He then reappeared in the 1 hour season 3 premiere in "Journey to Monkey King Castle."
Voiced by Jack Cygan.

The Fox King is a red fox in The Fox Kingdom. He creates magic bamboo forests to keep the bears away. He usually gets mad, and he couldn't get his sleep and talk to his friends, because of the dancing bears. The Fox King is voiced by James Siang'a.

The Foxes are red foxes that live in The Fox Kingdom. They sing loudly to annoy the Bear Queen. The Fox King's Guards wear Chinese Men's Hats and wear green.

The Bear Queen is a brown bear in The Bear Kingdom. She creates a moat to keep the foxes away. She is usually mad, and she couldn't get her sleep and talk to her friends, because of the singing foxes. The Bear Queen is voiced by Lucy Liu.

The Bears are brown bears that live in The Bear Kingdom. They dance to make the ground shake, and they anger the Fox King. The Bear Queen's guards wear knights' helmets and wear purple suited armor.

Dinosaur Rolling Egg Balls - It is not known what color or colors the balls were before they were re-painted as dinosaur eggs. They are a white-yellow color as Dinosaur egg-like. They are shaped like ovals and Kai-Lan and her friends use them in the final game of the "Dinosaur Games" olympics.